PENICILLIN 99 



et al., 1945). In addition to the cup assay method, penicillin titres can be 

 determined by serial dilution techniques, or by turbidimetric methods 

 (Joslyn, 1944; McMahan, 1944; and Trussell et al, 1947). Detailed in- 

 formation regarding the different techniques is contained in the papers 

 cited. 



Types of Penicillin 



Cultures of Penicillium notatum and P. chrysogenum commonly produce 

 two or more of four types of penicillin, which are generally referred to in 

 this country as F, G, X, and K and in Great Britain as I, II, III, and IV, 

 respectively (Benedict and Langlykke, 1947). Of these, penicillin F was 

 the first to be crystallized. Penicillin G, however, is more stable and is 

 generally produced in much greater amount. This type has gradually 

 come to represent the penicillin of commerce, which is today generally 

 marketed as crystalline penicillin G. PeniciUin K shows a greater activity 

 against many organisms in culture than penicillin G, but is chemically less 

 stable and is rapidly eliminated from, or destroyed in, the animal body. 

 It is of comparatively little value therapeutically (Eagle, 1946, 1947a, 

 1947b, 1947c, and Eagle and Musselman, 1946). The higher yielding 

 strains of penicillin-producing molds, such as X-1612 and Q-176, tend to 

 produce substantial amounts of penicillin K unless measures are taken to 

 prevent such development. It has been foiuid that the addition of phenyl- 

 acetic acid or phenylacetamide, or some other suitable adjuvant, to the 

 culture solution will markedly reduce the amount of penicillin K and en- 

 hance the production of penicillin G (Higuchi et al., 1946). Phenylacetic 

 acid as a constituent of the culture medium was first investigated by Moyer 

 and Coghill (1946c) as a possible means of increasing the total yield of 

 penicillin. Today it performs a much more important function in altering 

 the ratio of penicillins produced by the highest yielding strains. 



Penicillin X, or chloroform insoluble penicillin, has a relatively low activ- 

 ity against some test bacteria in agar plates but is retained in the animal 

 body longer than the other penicillins, hence, upon a unit basis represents 

 a more effective drug. In addition, some evidence has been published 

 (Welch, et al, 1944; Ory, et al, 1945; Flippin, et al, 1945; Libby and Holm- 

 berg, 1945) which indicates that penicillin X may combat infections that 

 have become resistant to the more common penicillin G. For this reason 

 it appeared desirable to find, or develop, some strain capable of producing 

 high yields of this penicillin in submerged culture. This was accomplished 

 by irradiating with ultra-violet light (fig. 32) a culture of Penicillium 

 chrysogenum, NRRL 1984, that had previously been found to be a good 

 "submerged" strain, and producing from it a biochemical mutation, desig- 

 nated NRRL 1984.N22, which formed penicillin X in 50 per cent yield 



